Presently available container drums are typically made of thermoplastic synthetic material, comprising at least one carrying and transport ring formed on the outer surface of the drum a short distance below the associated end surface of the drum. The ring comprises horizontal and vertical contact surfaces, that is, a first surface extending radially outwardly and a second surface extending parallel to the axis of the drum, for interfitting with the lift arms of conventional mechanized drum handling equipment. The drum may be produced entirely by the blow molding process, and the carrying and transport ring may be formed integrally with the shell and ends of the drum.
When lifting and transporting a drum, the arms of conventional mechanized drum handling equipment engage below the horizontal contact surface and behind the vertical contact surface of the carrying and transport ring. The total weight of the drum is transmitted to the lower lift arm via the horizontal contact surface, while the engagement of the upper lift arm behind the vertical contact surface prevents the drum from slipping off the lower arm.
The shell and ends of such drums may be produced integrally with the bearing and transport ring, e.g., by blow-molding. See U.S. Pat. Nos. 4,228,122 and 4,674,648. Alternatively, the bodies of such drums may be produced by the blow-molding process, while the end members and rings are produced by the injection-molding process. The injection-molded end members, with the bearing and transport rings formed thereon, are welded onto the body of the drum in a separate operation.
Because control of the welding step is difficult in this design, the carrying and transport rings are typically designed so that the critical weld zone created during the molding and forming process is largely relieved of bending forces. For this purpose, the carrying and transport ring is joined to the drum by way of a connecting web meeting the surface of the drum and joining the horizontal contact surface. The connecting web is designed so that it is stressed only by harmless tensile loads when the drum is lifted and transported by the ring.
To make the attachment as elastic as possible, the carrying and transport ring has been designed to meet the surface of the drum at an acute angle to the axis of the drum. An example of this design is shown in U.S. Pat, No. 4,674,648. In this design, the channel formed between the axially extending vertical surface of the carrying and transport ring and the adjacent conical surface section of the drum is essentially V-shaped in cross-section. The channel bottom is located in the plane of the horizontal contact surface of the carrying and transport ring. Hence, the space between the vertical contact surface and the conical surface section of the drum is very narrow, especially since the stacking forces which are produced upon stacking filled drums must be diverted by way of the conical surface into the cylindrical center section of the drum. The narrow groove requires that the ends of the upper arm of the drum handling equipment used have a special shape.